1. Field of the Invention
This invention relates to the art of automatic syringes, caulking guns, and similar devices used for dispensing repeatedly, precise, measured doses of liquid or other fluids from a barrel containing the liquid; and more particularly, the invention involves means for preventing dripping of liquid from the syringe after each dose is dispensed.
2. Background of the Invention
In my prior U.S. Pat. No. 4,678,107, I introduced the concept of adapting a syringe to prevent dripping, by providing an elastic concave disc or cap at the end of the plunger rod. The cap flattens out during discharge of liquid from the barrel. When forward driving movement of the plunger rod ceases, the cap reassumes its concave form to create a suction which draws and holds the liquid in the barrel to prevent dripping. When a syringe having a rigid seal or a pivoting stop at the driving end of the plunger rod is used, the elastic cap described in my prior patent above mentioned cannot be used. The use of a solid, rigid seal or pivotal stop at the end of the plunger is highly desirable to insure positive ejection of a required dose from the syringe. The present invention seeks to avoid replacing the solid seal in an automatic syringe by an elastic one because of the better control afforded when many doses are administered one after the other from an automatic syringe; and because it is desirable to keep the liquid in the barrel from contacting the elastic cap.